Our long range goal is to understand the extracellular functions of galectin-3 in the progression of breast cancer. The central hypothesis states that galectin-3 at moderate concentrations, modify cell surface properties which favor high adhesive interactions while at higher concentrations favor reduced adhesion of breast carcinoma cells to extracellular matrix (ECM) proteins. The hypothesis will be investigated through 3 specific aims which are; 1) to define the role of galectin-3 in the enhancement of adhesion of breast carcinoma cells to the extracellular matrix proteins, 2) to determine the mechanisms by which elevated concentrations of galectin-3 reduce adhesion of breast carcinoma cells to the extracellular matrix proteins, and 3) to assess the role of galectin-3 in mammary tumorigenesis. Confocal microscopy and Fluorescence resonance energy transfer approaches will be used to study integrin clustering and movement of lipid rafts/caveolae on the surface of breast epithelial cells in the absence and presence of galectin-3. The mobility of lipid and protein microdomains is likely to affect cell surface hydrophobicity which in turn may influence adhesive properties of the cells on hydrophobic surfaces. The binding interactions of liposomes containing integrins on their surfaces with extracellular matrix proteins, will be evaluated in the absence and presence of galectin-3. Polylactosamine residues will be enzymatically removed from these integrins and adhesive interactions evaluated again. Breast epithelial cells will also be treated with reagents like swansonine which reduce polylactosamine residues on the integrins and their adhesion to ECM evaluated in the absence and presence of galectin-3. Galectin-3 knockout mice will be crossed with transgenic mice expressing Polyoma virus middle T antigen (PymT) to obtain mice that are galectin-3 null and with propensity to form mammary tumors. These will be compared to galectin-3 wild type mice with the PymT+. The galectin-3 wild type mice are expected to develop more and larger tumors than the null mice. The mouse model of breast cancer will be used to directly address the rode of galectin-3 in mammary carcinogenesis and progression.